The inventive concepts relate to non-volatile memory devices, and more particularly, to methods of compensating for degradation of resistive memory devices.
Resistive memory devices such as phase change RAM (PRAM), resistive RAM (RRAM), and magnetic RAM (MRAM) are known as non-volatile memory devices. In such resistive memory devices, variable resistance devices, which store data according to changes in the condition of resistances, are used as memory cells. Resistive memory devices include cross-point type resistive memory devices. A cross-point type resistive memory device may be formed by placing the memory cells of the memory device at cross-points at which a plurality of bit lines and a plurality of word lines cross one another. A resistive memory device may access a memory cell therein by applying a voltage to two opposite terminals of the memory cell, and the accessed memory cell may store a logic “1 (set data)” (a low-resistance state) or a logic “0 (reset data)” (a high-resistance state) with reference to a threshold resistance of the memory cell.
A criterion in the resistive memory device is a retention time at which data may be preserved and an endurance level at which a normal operation may be performed without being worn out when writing data. Data retention and endurance of the resistive memory device may be dependent on circumstances that deteriorate characteristics of memory cells, for example, a high temperature and/or the number of program times. Due to degradation of the memory cells, a sensing margin between the set data of logic “1” and the reset data of logic “0” may decrease. Therefore, timing overhead, which means sensing of the set data or the reset data becomes less reliable or slower, or a plurality of bit errors may be caused. Degradation of the resistive memory device results in decrease in the capacity of a storage device including the resistive memory device.